High precision long term frequency/timing measurement plays a crucial role in engineering applications, such as, for example, in the fields of communications, electronics, and sensor systems. In applications ranging from measurement to frequency standards, precision is often limited by low frequency offset phase noise.
This noise can be attributed in part to “colored noise”, noise that varies as a function of frequency, such as 1/f3 noise. Colored noise in high frequency measurements can be caused by up-conversion of low frequency noise. For example, flicker noise can appear at both the fundamental and harmonic frequencies of frequency/timing blocks. Since colored noise presents a high correlation between adjacent measurement samples, it cannot be suppressed using conventional sample averaging methods.
High precision long term frequency/timing measurements are important in modern biosensors, such as in magnetic biosensor applications. Magnetic biosensors in the form of portable microarrays have been proposed to replace or augment conventional fluorescent sensors, which need bulky and expensive optical systems. Also, portable microarray biosensors are promising for Point-of-Care (POC) medical applications, such as disease detection, control, and monitoring, where the key technical challenges are hand-held portability, high sensitivity, battery-level power consumption, and low cost.
However, magnetic sensors as reported thus far require external bias magnetic fields and/or complicated post-processing, limiting their form factor and cost. An ultrasensitive frequency-shift sensing scheme using high precision frequency/timing measurements has been proposed to address these issues. Yet, phase noise, particularly low frequency noise in portable microarray magnetic biosensor prototypes continues to be problematic.
What is needed, therefore, is a method and apparatus to substantially suppress phase noise power in frequency/timing measurements that does not significantly increase cost and power consumption.